1. Field of the Invention
The present invention relates to a guide-bar device for a single spindle lathe, comprising a sectional carrier on which is removably secured a guiding element for bar stock to be machined. The advance of the bar stock towards the lathe is controlled by a push-piston located in the guiding element. The device further comprises a distribution of oil under pressure, the oil being injected on the one hand at the rear of the push-piston for controlling its advance in the guiding tube and on the other hand between the bar stock to machined and the internal wall of the guiding element in order to create a hydrodynamic bearing for supporting the bar stock to be machined which is set into rotation by the head stock of the lathe.
2. Related Art
Such a guide-bar device is known from U.S. Pat. No. 4,507,992 of the same applicant. The known device comprises a U-shaped sectional carrier open at the top in which are mounted semi-cylindrical seats provided for sustaining the guiding tube. The guiding tube is removably secured on the seats by means of articulated clamps gripped by a nut. Such a device has numerous disadvantages. It is expensive to manufacture, because it comprises many parts which must be very carefully assembled in order to guarantee precise alignment and good support for the guiding tube. Furthermore, the rigidity and the stability of an open section is not ideal. The exchange of the guiding tube is too slow due to the presence of the clamps gripped by a nut. The oil which flows out from the front part of the guiding tube is returned to the hydraulic group by the U-shaped sectional carrier (open at the top) so that there is a risk of contamination of the oil by impurities and dust from the outside. Further, a lack of stability of the device causes undesirable vibrations which are transmitted to the bar stock in progress of machining which produces a poor machining quality.
The Swiss Patent CH 514 381 relates to a device for providing an automatic lathe with a bar stock to be machined. The device comprises a guiding tube for the bar stock and a push-piston for advancing the bar stock in its guiding-tube towards the lathe, the push-piston being engaged with play in the guiding-tube and connected by its back part to a source of oil under pressure. The oil flows through the play from the back part to the front part of the push-piston for soaking the bar stock. In this device, the oil soaking the bar stock must necessarily flow through the play from the back part to the front part of the push-piston so that the flow of oil under pressure cannot be controlled with sufficient precision for allowing high speeds of rotation of the bar stock.
The Swiss Patent CH 576 304 described a device of the same kind as the preceding one for providing an automatic lathe with bar stock to be machined. The push-piston which is engaged with play in the guiding-tube comprises an internal passage for the oil, this passage being parallel to the passage corresponding to the play between the push-piston and the guiding-tube and also being capable of adjustment by an adjusting means. However, the adjustment of the flow of oil under pressure delivered by the internal passage can only be accomplished by manual action on a valve of the push-piston when the machine is stopped and the push-piston is fully withdrawn from the guiding tube. This does not contribute to reduce the dead time of the machine.
The French patent application No. FR 2 512 365 relates to a tool-maker's lathe. The two head stocks each comprise a closed cross section. However, such a closed section is not foreseen for sustaining a guiding-tube nor for providing a distribution of oil under pressure.